The present invention relates generally to transmissions for use in four-wheel drive vehicles. More particularly, the present invention is directed to a transmission having a multi-speed geartrain and a power transfer arrangement contained in a single gearbox.
As is known, the majority of four-wheel drive vehicles are equipped with a transfer case mounted to a multi-speed transmission for directing power to all four wheels. To accommodate different road surfaces and conditions, many transfer cases are equipped with a gear reduction unit that can be shifted by the vehicle operator for establishing high-range (i.e., direct) and low-range (i.e., reduced ratio) four-wheel drive modes. Likewise, some transfer cases are equipped with an interaxle differential for delivering drive torque to the front and rear drivelines of the four-wheel drive vehicle while permitting speed differentiation therebetween.
In an effort to minimize the overall size of the drivetrain used in four-wheel drive vehicles, it has been proposed to utilize a transmission of a transaxle-type normally used to drive the front wheels of a front wheel drive vehicle as a four-wheel drive geartrain. In particular, British Patent No. 2,035,930 to Jones et al. teaches of rotating the front wheel drivetrain (i.e., engine and transaxle) such that the transaxle outputs can be interconnected to the front and rear drivelines of the motor vehicle. While such an arrangement may provide an economical drivetrain layout for a full-time four-wheel drive vehicle, the practical applications for such an arrangement are severely limited. For instance, such an arrangement does not permit the vehicle operator to selectively shift between high and low four-wheel drive modes.
Accordingly, the need exists for a transmission which can be used in most conventional four-wheel drive applications and which permits the vehicle operator to selectively shift between the available gear ratios and drive modes.